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Abstract. Using 11-year-long K Doppler lidar observations of temperatureprofiles in the mesosphere and lower thermosphere (MLT) between 85 and100 km, conducted at the Arecibo Observatory, Puerto Rico(18.35^∘ N, 66.75^∘ W), seasonalvariations of mean temperature, the squared Brunt–Väisäläfrequency, N², and the gravity wave potential energy (GWPE) are estimated in a compositeyear. The following unique features are obtained. (1) The mean temperaturestructure shows similar characteristics to an earlier report based on a smallerdataset. (2) Temperature inversion layers (TILs) occur at 94–96 km inspring, at ∼92 km in summer, and at ∼91 km in early autumn.(3) The first complete range-resolved climatology of GWPE derived from temperature data in the tropical MLT exhibits analtitude-dependent combination of annual oscillation (AO) and semiannualoscillation (SAO). The maximum occurs in spring and the minimum in summer, and asecond maximum is in autumn and a second minimum in winter. (4) The GWPE perunit volume reduces below ∼97 km altitude in all seasons. Thereduction of GWPE is significant at and below the TILs but becomes faintabove; this provides strong support for the mechanism that the formation ofupper mesospheric TILs is mainly due to the reduction of GWPE. The climatologyof GWPE shows an indeed pronounced altitudinal and temporal correlation withthe wind field in the tropical mesopause region published in the literature.This suggests the GW activity in the tropical mesopause region should bemanifested mainly by the filtering effect of the critical level of the localbackground wind and the energy conversion due to local dynamical instability.